OpenCasCade – 贴纹理

前言

因为项目需要，所以最近研究了下给用OpenCasCade库创建的模型贴纹理的问题。因为网上没找到相关的文章，特此记录下来。

官方示例

本文中的代码是完全仿照官方示例（All-vc10 中的 Viewer3d）所写的，筒子们可以自己去研究一下这块代码，如图：

然后看下官方示例的贴纹理效果：

代码解读

这里为简单起见，只解读图一中 Bottle 的代码，代码的作用，请仔细阅读注释：

sampleBottle函数（创建Bottle，调用Texturize函数）：

//通过载入brep文件，创建bottle，并贴纹理

void TexturesExt_Presentation::sampleBottle()

{

//创建一个bottle

TopoDS_Shape aShape;

if (!loadShape(aShape, "bottle.brep"))

return;

// resize and move the shape to the center of the viewer 这块代码对纹理显示无贡献

gp_Trsf aTrsf1, aTrsf2;

aTrsf1.SetScale(gp_Pnt(0,0,0), /*0.8*/0.1); //对 bottle 进行缩放

aTrsf2.SetTranslation(gp_Pnt(0,0,0),gp_Pnt(0,0,-20));

aTrsf1.Multiply(aTrsf2);

BRepBuilderAPI_Transform Transformer(aTrsf1);

Transformer.Perform(aShape);

aShape = Transformer.Shape();

TopTools_IndexedMapOfShape aFaces;

// 函数原型：static void TopExp::MapShapes(const TopoDS_Shape& S, const TopAbs_ShapeEnum T, TopTools_IndexedMapOfShape& M)

// 第二个参数： TopAbs_ShapeEnum 是一个枚举类型，读者需要自己去读一下

// Tool to explore a topological data structure. Stores in the map <M> all the sub-shapes of <S> of type <T>.

TopExp::MapShapes(aShape, TopAbs_FACE, aFaces);

//没有这几句代码则只显示指定贴了纹理的那些FACE，不显示瓶子整体。但同样，这段对纹理的显示没有任何贡献。

//display original shape in shaded display mode

Handle_AIS_Shape aShapeIO = drawShape(aShape, Graphic3d_NOM_BRASS, Standard_False);

getAISContext()->SetDisplayMode(aShapeIO, AIS_Shaded, Standard_False);

// Set increased polygon offset for the main shape to avoid depth collision with textured faces

aShapeIO->SetPolygonOffsets(Aspect_POM_Fill, 1.5, 0.5);

DISP(aShapeIO); // #define DISP(OBJ) getAISContext()->Display((OBJ), Standard_False)

//指定需要贴纹理的FACE，设置相关参数

Handle_AIS_TexturedShape aTFace1 = Texturize(aFaces(16), "carrelage1.gif", 1, 1, 3, 2);

DISP(aTFace1);

Handle_AIS_TexturedShape aTFace2 = Texturize(aFaces(21), "carrelage1.gif", 1, 1, 3, 2);

DISP(aTFace2);

//更新视图

getViewer()->Update();

}

Texturize函数（贴纹理）：

Handle_AIS_TexturedShape TexturesExt_Presentation::Texturize(const TopoDS_Shape& aShape,

TCollection_AsciiString aTFileName,

Standard_Real toScaleU,

Standard_Real toScaleV,

Standard_Real toRepeatU,

Standard_Real toRepeatV,

Standard_Real originU,

Standard_Real originV)

{

//create a textured presentation object for aShape

//AIS_TexturedShape 是一个非常重要的类！下面是官方文档中的说明

//This class allows to map textures on shapes. Presentations modes AIS_WireFrame (0) and AIS_Shaded (1) behave in the same manner as in AIS_Shape

//whilst new modes 2 (bounding box) and 3 (texture mapping) extends it functionality.

//The texture itself is parametrized in (0,1)x(0,1). Each face of a shape located in UV space is provided with these parameters:

//•Umin - starting position in U

//•Umax - ending position in U

//•Vmin - starting position in V

//•Vmax - ending position in V

//Each face is triangulated and a texel is assigned to each node. Facets are then filled using a linear interpolation of texture between each 'three texels'.

//User can act on:

//•the number of occurrences of the texture on the face

//•the position of the origin of the texture

//•the scale factor of the texture

Handle_AIS_TexturedShape aTShape = new AIS_TexturedShape(aShape);

TCollection_AsciiString TFileName;

//load texture from file if it is not an integer value

//integer value indicates a number of texture in predefined TexturesExt enumeration

CString initfile(((OCC_App*) AfxGetApp())->GetInitDataDir());

initfile += "\\Data\\";

if (!aTFileName.IsIntegerValue())

{

initfile += aTFileName.ToCString();

}

aTShape->SetTextureFileName((Standard_CString)(LPCTSTR)initfile);

// do other initialization of AIS_TexturedShape

aTShape->SetTextureMapOn();

aTShape->SetTextureScale(Standard_True, toScaleU, toScaleV);

aTShape->SetTextureRepeat(Standard_True, toRepeatU, toRepeatV);

aTShape->SetTextureOrigin(Standard_True, originU, originV);

aTShape->SetDisplayMode(3); // mode 3 is "textured" mode，参见上面AIS_TexturedShape类的解释

return aTShape;

}

至此，就可以实现上图中显示的Bottle效果。同学们可以自己创建一个简单的 box 来尝试一下，这里我给个简单的示例：

void CneedAVView::MakeBottle()

{

TopoDS_Shape aRes = BRepPrimAPI_MakeBox(gp_Pnt(0,0,0),555,555,555).Shape();

TopTools_IndexedMapOfShape aFaces;

TopExp::MapShapes(aRes, TopAbs_FACE, aFaces);

Handle(AIS_TexturedShape) aTFace1 = Texturize(aFaces(1), "./carrelage1.gif", 1, 1, 3, 2);

DISP(aTFace1);

Handle(AIS_TexturedShape) aTFace2 = Texturize(aFaces(2), "./carrelage1.gif", 1, 1, 3, 2); //16 21 3 2

DISP(aTFace2);

Handle(AIS_TexturedShape) aTFace5 = Texturize(aFaces(5), "./carrelage1.gif", 1, 1, 3, 2);

DISP(aTFace5);

myView->Update();

}

Handle(AIS_TexturedShape) CneedAVView::Texturize(const TopoDS_Shape& aShape,

TCollection_AsciiString aTFileName,

Standard_Real toScaleU,

Standard_Real toScaleV,

Standard_Real toRepeatU,

Standard_Real toRepeatV,

Standard_Real originU,

Standard_Real originV)

{

// create a textured presentation object for aShape

Handle(AIS_TexturedShape) aTShape = new AIS_TexturedShape(aShape);

//此地纯属偷懒

CString temp("d://program files//opencascade-6.7.1//samples//mfc//standard//04_viewer3d//data//cookerplate.gif");

aTShape->SetTextureFileName((Standard_CString)(LPCTSTR)temp);

// do other initialization of AIS_TexturedShape

aTShape->SetTextureMapOn();

aTShape->SetTextureScale(Standard_True, toScaleU, toScaleV);

aTShape->SetTextureRepeat(Standard_True, toRepeatU, toRepeatV);

aTShape->SetTextureOrigin(Standard_True, originU, originV);

aTShape->SetDisplayMode(3); // mode 3 is "textured" mode

return aTShape;

}

也许你发现这样还是看不到显示的纹理！

后来发现，需要设置这样关键的一句

1	myView->SetSurfaceDetail(V3d_TEX_ALL);

函数原型：void V3d_View::SetSurfaceDetail(const V3d_TypeOfSurfaceDetail SurfaceDetail)

功能：select the kind of rendering for texture mapping no texture mapping by default

其中 V3d_TypeOfSurfaceDetail 是一个枚举类

enum V3d_TypeOfSurfaceDetail

Modes of visualization for objects in a view.

·V3d_TEX_NONE: no texture mapping,

·V3d_TEX_ENVIRONMENT: environment mapping only,

·V3d_TEX_ALL: environment and texture mapping.

Enumerator：

·V3d_TEX_NONE

·V3d_TEX_ENVIRONMENT

·V3d_TEX_ALL

如官方文档中所述：

1	no texture mapping by default

所以我们要显示的把参数设置为：V3d_TEX_ALL

如此，你就可以看到自己贴的纹理了，效果图如下（因为我省略了一些函数所以这里只显示了贴纹理的面（见 sampleBottle 函数中所述））：

至此，OpenCasCade的中的贴纹理就搞定了，想了解更多，请自行阅读官方示例。

感谢原作者的知识分享。

转自按地址：http://www.zyh1690.org/opencascade-texture/